Method for signal transmission in a communication system between a mobile radio transmission/reception device and a stationary radio transmission/reception device

ABSTRACT

The radio area to be covered by the stationary radio transmission/reception device, for example of the base station of a cordless telephone, is illuminated by two or more directional antennas ( 3, 4 ) respectively covering a radio sub-area thereof, whereby that respective directional antenna in whose radio sub-area the mobile radio transmission/reception means, i.e., for example, the mobile part of the cordless telephone, is located is activated (antenna diversity). The method and apparatus can be advantageously utilized in cordless telephones.

BACKGROUND OF THE INVENTION

The invention is directed to a method for signal transmission in acommunication system between a mobile radio and a base station. Theinvention is also directed to an apparatus for the implementation ofthis method.

The range in a wireless communication system, for example a cordlesstelephone, that is composed of a stationary and of a mobile radiotransmission/reception means is defined essentially by its transmissionpower and its receiver sensitivity. The transmission power is therebyusually uniformly emitted in all directions, i.e. nearly spherically, inorder, first, to be universally employable in every environment and,second, to achieve the same range in every direction. When, however, anindividual is point in time is considered, then—from the point of viewof the stationary radio transmission/reception means, i.e. of the basestation of the cordless telephone in the example—only a fraction of thetransmission energy is emitted in the direction of the mobile radiotransmission/reception means, i.e. the mobile part of the cordlesstelephone in the example. The great majority of the transmission energy,by contrast, is not utilized and can even have an interfering effect onexternal devices.

A stationary radio transmission/reception means with a sharply bundlingdirection al antenna would be desirable that emits the available energyconcentrated in precisely that direction in which the mobile radiotransmission/reception means is situated at the moment. However, a notinsubstantial outlay for locating the mobile means, i.e. the mobile partof a cordless telephone in the example, and for the exact alignment ofthe directional antenna would be required therefor.

SUMMARY OF THE INVENTION

An object of the invention is to create a considerably less involvedpossibility of improving the transmission behavior between the mobileand the stationary radio transmission/reception means of atelecommunication system, particularly of a cordless telephone.

In general terms the present invention is a method for signaltransmission in a communication system between a mobile radiotransmission/reception means provided with an antenna means,particularly the mobile part of a cordless telephone, and a stationaryradio transmission/reception means likewise provided with an antennameans, particularly the base station of a cordless telephone. The radioarea to be covered by the stationary radio transmission/reception meansis illuminated by two or more directional antennas, each respectivelycovering a radio sub-area thereof. The directional antennas form theantenna means of the stationary radio transmission/reception means. Inthe fashion of antenna diversity, the directional antenna is activatedin whose radio sub-area the mobile radio transmission/reception means islocated.

The sum of the radio sub-areas covered by all directional antennas ofthe stationary radio transmission/reception means forms an at leastapproximately point-symmetrical radio area.

A manually implemented alignability of the directional antennas, so thatthe radio area they illuminate can be matched to the respectivelyexisting environment, for example a building.

The selection of the directional antenna to be respectively activated isundertaken on the basis of comparative measurements of the receptionfield strength in the stationary radio transmission/reception means.

In general terms the present invention is also an apparatus for theimplementation of the above-described method. The antenna means of thestationary radio transmission/reception means is equipped with two ormore directional antennas, whereof each covers a radio sub-area of theradio area to be acquired by the stationary radio transmission/receptionmeans. The directional antenna in whose radio sub-area the mobile radiotransmission/reception means is located is respectively activated.

Advantageous developments of this embodiment of the present inventionare as follows.

A direction adjustment means is provided for the directional antennas ofthe stationary radio transmission/reception means.

A measuring means with which the reception field strengths of thesignals incident via the individual directional antennas and coming froma mobile radio transmission/reception means are measured is provided inthe radio transmission/reception means. A comparison and selection meansis provided that compares the reception field strengths and determinesthe highest thereof, so that the directional antenna at which thehighest reception field strength is present is activated.

The directional antennas of the stationary radio transmission/receptionmeans are formed by what are referred to as quick-heading beam antennasthat are respectively composed of a vertical half-wave radiator withfour parasitic elements that are arranged at the distance of0.15λ(λ=wavelength) each from the half-wave radiator and whose lengthsare switched such that they optionally act either as directors or asreflectors.

This form of antenna diversity, however, is to be distinguished fromthat utilized to combat fading effects and that is disclosed by GermanUtility Model 92 14 455. When the antenna diversity method fashionedaccording to the invention is implemented with directional antennas atthe side of the stationary radio transmission/reception means of thesystem, then the employment of an anti-fading antenna diversityarrangement is not possible at the side of the stationarytransmission/reception means, i.e., for example, at the side of the basestation of a cordless telephone, unless each directional antenna weredoubly implemented. The function of the known anti-fading antennadiversity, however, can be displaced into the mobile radiotransmission/reception means of the system, i.e. into the mobile part ofa cordless telephone in the example, or, respectively, this function canbe limited to the mobile part.

BRIEF DESCRIPTION OF THE DRAWINGS

The features of the present invention which are believed to be novel,are set forth with particularity in the appended claims. The invention,together with further objects and advantages, may best be understood byreference to the following description taken in conjunction with theaccompanying drawings, in the several Figures of which like referencenumerals identify like elements, and in which:

FIGS. 1-9 depict various radiation distributions in planar sectionsassociated with the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS.

FIG. 1 shows the known case wherein the transmission power of astationary transmission/reception means, for example the base station ofa cordless telephone, is uniformly output in the environment thereofwith an omnidirectional antenna 1 or, respectively, radio signalsderiving from a mobile radio transmission/reception means, for example,thus, from the mobile part of the cordless telephone, are uniformlyomnidirectionally received by this stationary radiotransmission/reception means. The antenna 1 thus has what is referred toas an omnidirectional characteristic 2 with which an identical range Ais achieved in every direction. When viewing only a single point intime, the stationary radio transmission/reception means only emits afraction of the transmission energy in the direction of the mobile radiotransmission/reception means, by contrast whereto the great majority ofthe transmission energy is not exploited.

FIG. 2, compared thereto, shows the division of the region shown withbroken lines and having the range A into two sub-areas. Each of thesetwo individual sub-areas is illuminated by the stationary radiotransmission/reception means with a respective antenna 3 or,respectively, 4 having directional characteristic 5 or, respectively, 6.In the fashion of antenna diversity, that of the two directionalantennas 3 and 4 in which the mobile radio transmission/reception meansis located is thereby respectively active. Since the range A remains thesame in the case illustrated in FIG. 2, the transmission power and thereceiver sensitivity of the stationary means can be reduced.

A comparison of FIG. 3, in which, agreeing with FIG. 1, theomnidirectional characteristics 2 of an antenna 1 of a stationary radiotransmission/reception means, i.e., for example, of the base station ofa cordless telephone, having the range A is shown to FIG. 4, in whichthe same energy is emitted respectively upon activation via respectivelyone of the two directional antennas 7 and 8 (transmission case) or,respectively, the same receiver sensitivity (reception case) exists asin the case according to FIG. 3, shows that the range A' then achievedis increased by the factor {square root over (2)} compared to the rangeA of FIG. 3 given free space propagation. FIGS. 3 and 4 thus shown thegain in range to be expected given an antenna diversity implementedaccording to the invention and unmodified transmission power / receiversensitivity. In the example of FIG. 4, the antenna characteristic 9(shown with solid lines) of the directional antenna 7 is activated atthe illustrated point in time, by contrast whereto the antennacharacteristic 10 (shown with broken lines) of the directional antennais not active at the moment since the mobile radiotransmission/reception means is located in the radio sub-area with therange A' covered by the directional antenna 7.

It can thus be stated that a concentration of the transmission poweronto a hemisphere corresponds to the doubling of the power emitted intothis hemisphere. A doubling of the transmission power thus correspondsto an increase of the range by the factor {square root over (2)}.

FIG. 10 is a block diagram depicting the embodiment of the presentinvention. Significant advantages of the method according to theinvention are explained on the basis of FIGS. 5 through 9 for a cordlesstelephone composed of a base station 11 and a mobile part 12. In thestandard case, which is shown in FIG. 5, the base station 11 and themobile part 12 respectively comprise an antenna with omnidirectionalcharacteristics 13 or, respectively, 14. The distance B between the basestation 11 and the mobile part 12 is dimensioned such in this examplethat radio communication can still just be implemented given the rangesthat are provided.

FIG. 6 shows the case of how, given unmodified transmission power or,respectively, receiver sensitivity compared to FIG. 5, the range of thecommunication system, i.e. of the cordless telephone in the illustratedcase, is increased according to the invention by the factor {square rootover (2)} given free space propagation by employing an antenna having adirectional characteristic 15 in the base station 11. The mobile part 12is still reached by the base station 11 when their spacing isconsiderably greater than the distance B in the case of FIG. 5, which isthe actual condition before the invention. When the method of theinvention is not utilized for increasing the range, as in FIG. 6, thedemands made of the receiver sensitivity of the base station 11 and ofthe mobile part 12 can be reduced, possibilities for cost reductionusually deriving therefrom. This case is shown in FIG. 7, wherein thearea in which the transmission signal does not fall below a standardlevel is respectively shown with a solid line and the area in which asignal can be received with at least standard level is shown with brokenlines. Here, thus, the base station 11 transmits with a radiation powerincreased by the gain of the directional characteristic 16, so that thesensitivity (shown with broken lines) of the receiver of the mobile part12 can be reduced. Due to the employment of a directional antenna in thebase station 11, conversely, the receiver sensitivity thereof canlikewise be reduced given transmission of signals on the part of themobile part 12, since the reduced directional characteristic 17 (shownwith broken lines) still suffices for faultlessly receiving signalstransmitted from the mobile part 10.

When the method according to the invention is not utilized forincreasing the range, then—alternatively to the reduction of thereceiver sensitivity that was explained on the basis of FIG. 7—thetransmission power in the base station 11 and in the mobile part 12 canbe reduced. This case is shown in FIG. 8. Due to the lower energyconsumption, this leads to an increase in the operating duration of thebattery-powered mobile part 12. In FIG. 8, the area in which thetransmission signal does not fall below a standard level is shown with asolid line, and the area in which a signal can be received with at leaststandard level is shown with a broken line. In the case of transmissionson the part of the base station 11, a lower transmission power sufficesfor reaching the mobile part 12 in terms of radio due to the employmentof a directional characteristic 18. When, by contrast, the base stationis to receive, a diminished transmission power of the mobile part 12suffices since the base station 11 exhibits enhanced receptionsensitivity with the directional characteristic 19 shown with brokenlines.

Generally valid is that a reduction of the perturbing radiation derivesdue to the employment of the method according to the invention. Nopower, namely, is beamed out into the sub-area in which the mobile part12 is not located, i.e. external devices within this sub-area are notdisturbed. When the method of the invention is not employed forincreasing the range, then—as was already stated above—the transmissionpower of the mobile part 12 can be reduced. The interfering effect onother systems in the environment of the mobile part 12 is therebyreduced.

With reference to FIG. 9, it shall also be explained below that there isalso the possibility of uniting the various advantages of the inventivemethod in the mobile part 12.

The transmission power and the receiver sensitivity of the base station11 remain unmodified up to the antenna pick-up point. Due to thedirectional characteristic 20 of the directional antenna, which yields again in a radio sub-area, however, both the radiation power as well asthe receiver sensitivity are effectively enhanced in this radiosub-area.

The “greater” effective transmission power of the base station 11enables the reduction of the receiver sensitivity of the mobile part 12.Since it is provided that a base station 11 maintains contact to aplurality of mobile parts, the cost-saving in the receiver of the mobilepart 12 takes multiple effect.

The “greater” effective sensitivity of the base station 11 also enablesthe reduction of the transmission power of the mobile part 12. As aresult, first, the power consumption of the mobile part 12 is reduced,i.e. a longer operating duration derives or, however, one can managewith a smaller and, therefore, more beneficial battery. On the otherhand, the interfering effect on other system in the proximity of themobile part 12 is reduced.

The directional antenna or antennas of the stationary radiotransmission/reception means can be expediently differently set with adirection adjustment means.

What are referred to as quick-heading beam antennas can beadvantageously employed as adjustable directional antennas; these are tobe viewed as a development of the vertical half-wave beam antenna andare respectively composed of a vertical half-wave radiator with fourparasitic elements that are arranged at the distance of 0.15λ(λ=wavelength) each from the half-wave radiator and whose lengths areswitched such that they optionally act either as directors or asreflectors. What is achieved in this way is that the beam antenna sweepsall directions with its principal radiation due to appropriate switchingwithout having to rotate the antenna. In terms of its effect, thequick-heading beam antenna roughly corresponds to a 3-element Yagiantenna.

The invention is not limited to the particular details of the method andapparatus depicted and other modifications and applications arecontemplated. Certain other changes may be made in the above describedmethod and apparatus without departing from the true spirit and scope ofthe invention herein involved. It is intended, therefore, that thesubject matter in the above depiction shall be interpreted asillustrative and not in a limiting sense.

What is claimed is:
 1. A method for signal transmission in acommunication system between a mobile radio transmission/receptiondevice having a mobile antenna device, and a stationary radiotransmission/reception device having a stationary antenna device, themethod comprising the steps of: illuminating a radio area to be coveredby the stationary radio transmission/reception device by at least twoindividual directional antennas, the at least two individual directionalantennas forming the stationary antenna device; providing radiosub-areas of the radio area; covering each respective radio sub-area ofthe radio area with a respective one of the at least two individualdirectional antennas; and activating in antenna diversity fashion arespective one of the at least two individual directional antennas inwhose respective radio sub-area the mobile radio transmission/receptiondevice is located, wherein only one of the at least two individualdirectional antennas is activated at any one point in time for bothtransmitting and receiving data to and from the mobile antenna device.2. The method according to claim 1, wherein a sum of the radio sub-areascovered by all of the directional antennas of the stationary radiotransmission/reception device forms an at least approximatelypoint-symmetrical radio area.
 3. The method according to claim 1,wherein the method further comprises the step of manually aligning thedirectional antennas, so that the radio area illuminated is matched toan existing environment.
 4. The method according to claim 1, wherein themethod further comprises the step of selecting one of the directionalantennas to be respectively activated based on comparative measurementsof reception field strength in the stationary radiotransmission/reception device.
 5. A method for signal transmission in acommunication system between a mobile radio transmission/receptiondevice having a mobile antenna device, and a stationary radiotransmission/reception device having a stationary antenna device, themethod comprising the steps of: illuminating a radio area to be coveredby the stationary radio transmission/reception device by at least twoindividual directional antennas, the at least two individual directionalantennas forming the stationary antenna device; providing radiosub-areas of the radio area; covering each respective radio sub-area ofthe radio area with a respective one of the at least two individualdirectional antennas; activating in antenna diversity fashion arespective one of the at least two individual directional antennas inwhose respective radio sub-areas the mobile radio transmission/receptiondevice is located, wherein only one of the at least two individualdirectional antennas is activated at any one point in time for bothtransmitting and receiving data to and from the mobile antenna device;and wherein the mobile radio transmission/reception device is a mobiletelephone, and the stationary radio transmission/reception device is abase station.
 6. The method according to claim 5, wherein a sum of theradio sub-areas covered by all of the directional antennas of thestationary radio transmission/reception device forms an at leastapproximately point-symmetrical radio area.
 7. The method according toclaim 5, wherein the method further comprises the step of manuallyaligning the directional antennas, so that the radio area illuminated ismatched to an existing environment.
 8. The method according to claim 5,wherein the method further comprises the step of selecting one of thedirectional antennas to be respectively activated based on comparativemeasurements of reception field strength in the stationary radiotransmission/reception device.
 9. An apparatus for signal transmissionin a communication system between a mobile radio transmission/receptiondevice and a stationary radio transmission/reception device, theapparatus comprising: a mobile antenna device on the mobile radiotransmission/reception device; and a stationary antenna device on thestationary radio transmission/reception device, the stationary antennadevice formed of at least two individual directional antennas whichtogether illuminate a radio area to be covered by the stationary radiotransmission/reception device, each of the at least two individualdirectional antennas respectively covering a radio sub-area of the radioarea to be covered by the stationary radio transmission/receptiondevice, wherein a respective one of the at least two individualdirectional antennas in whose respective radio sub-area the mobile radiotransmission/reception device is located is respectively activated inantenna diversity fashion, wherein only one of the at least twoindividual directional antennas is activated at any one point in timefor both transmitting and receiving data to and from the mobile antennadevice.
 10. The apparatus according to claim 9, wherein the apparatusfurther comprises: a direction adjustment device for the directionalantennas of the stationary radio transmission/reception device.
 11. Theapparatus according to claim 7, wherein the apparatus further comprises:a measuring device with which respective reception field strengths ofsignals incident via each of the directional antennas and coming from arespective mobile radio transmission/reception device are measured inthe stationary radio transmission/reception devices wherein a comparisonand selection device compares the reception field strengths anddetermines a highest thereof, so that the respective one directionalantenna at which the highest reception field strength is present isactivated.
 12. The apparatus according to claim 9, wherein thedirectional antennas of the stationary radio transmission/receptiondevice are quick-heading beam antennas that are respectively composed ofa vertical half-wave radiator with four parasitic elements that arearranged at a distance of 0.15 λ, where λ is a wavelength each from thehalf-wave radiator and whose lengths are switched such that the elementsoptionally act either as directors or as reflectors.